imx-drm: update and fix imx6 DT descriptions for v3 HDMI driver

Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Reviewed-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/boot/dts/imx6dl.dtsi

@@ -90,5 +90,6 @@
 };
 
 &hdmi {
+	compatible = "fsl,imx6dl-hdmi";
 	crtcs = <&ipu1 0>, <&ipu1 1>;
-}
+};